(a) Field of the Invention
The present invention relates to a distance measuring method. Particularly the present invention relates to a distance measuring method in an impulse-based wireless communication system.
(b) Description of the Related Art
Recently, an impulse-based wireless technology that consumes low power and has a distance estimating function has gained interest as a promising technology, such as being adopted as a physical layer technology of the Institute of Electrical and Electronics Engineers (EEE) 802.15.4a that is an international standard of a low-speed positioning wireless personal area network (WPAN).
As the impulse-based distance estimating method, there is time of arrival (hereinafter referred to as “TOA”) that estimates a distance by measuring propagation transmission time between two nodes.
A one-way ranging (OWR) method that transmits messages between two synchronized nodes and a two-way ranging (TWR) method that transmits and receives messages between two asynchronized nodes can be applied to the TOA method. It is difficult to achieve network synchronization between nodes in IEEE 802.15.4a. As a result, the TWR method is adopted as a basic distance estimating method.
The TWR method has a disadvantage of being considerably affected by a clock frequency offset (hereinafter referred to as “CFO”) when estimating a distance between nodes. Herein, when a difference in CFO between nodes is large, response time is long and TOA estimation error is thus increased.
In order to solve the disadvantage of the TWR method being sensitive to CFO, a symmetric double-sided TWR (SDS-TWR) method has been proposed. However, the SDS-TWR method has a problem in that in order to reduce the effect of CFO, more packets should be transmitted and received in the TWR method. Further, when the positioning is performed based on the SDS-TWR method, there is a disadvantage in that considerable load is applied to the network.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.